This study is aimed at determining if premenopausal women taking Tamoxifen are at increased risk for developing osteoporosis. The study will use human monocyte cultures derived from cells obtained from volunteers of the OB/GYN and endocrine clinics. Tamoxifen may have different effects on bone resorption depending on the estrogen environment. After menopause, natural or surgical, it appears to inhibit bone resorption. However, in vitro studies in the presence of estrogen indicate that Tamoxifen inhibits the beneficial effects of estrogen on bone metabolism. This in vitro monocyte culture study will evaluate the effect of Tamoxifen on the production of two substances, the cytokines interleukin 1 B and interleukin-6 produced during bone metabolism. Specifically, it will be determined if Tamoxifen alone will decrease IL-I mRNA and protein productions in a dose responsive manner using a reverse transcriptase-polymerase chain reaction and if Tamoxifen in the presence of estradiol will negate the effect of estradiol on IL-I mRNA and protein production. IL-I will be measured by an enzyme linked immunosorbent assay.